1. Field of the Invention
This invention relates generally to classification apparatus used in placer mining operations, and more particularly to continuous flow apparatus for classification and specific gravity separation of relatively fine, heavy sands, particularly precious metal-bearing sands, from gravel and dirt aggregate.
2. Description of the Prior Art
Precious metals, such as gold, have been recovered from river bed gravel formations by the use of sluice boxes. A conventional sluice box comprises an elongated channel or trough having spaced, upstanding, transversely extending barriers or "riffles" on its bottom, the width of the spaces between the riffles conventionally being much greater than the thickness of the riffles, and each riffle commonly having a flange on its top edge which extends in the downstream direction. The sluice box is inclined and a stream of water is caused to flow therein with the gravel from which the precious metal is to be recovered being introduced at the upper end. The flow of water carries the lighter materials over the riffles whereas, the heavier gold-bearing sands accumulate behind the riffles and are periodically removed therefrom. The lighter and larger components of the gravel aggregate discharged from the sluice box are referred to as "tailings". Conventional classification apparatus commonly referred to as "grizzley", which merely separates or "classifies" smaller from larger particulate material, has commonly been employed ahead of a sluice box, in order preliminarily to remove the larger components of the aggregate.
Prior apparatus for recovering precious metals; i.e., conventional sluice boxes and classification apparatus, has been inefficient in that the tailings have included a considerable quantity of heavier, gold-bearing sands. In the past, efforts to recover on a continuous flow basis a higher proportion of the fine, heavy gold-bearing sands have been largely unsuccessful. Further, in the past, economics has not warranted recovery of the gold contained in such tailings, nor has it warranted efforts to recover gold from river bottoms having a lower gold content.
The dramatic increase in the price of gold and other precious metals now makes it desirable to provide more efficient apparatus for rapidly separating relatively fine, heavy precious metal-bearing sands from gravel and dirt aggregate in a continuous flow manner, and it is further desirable to provide such apparatus which is readily adjustable to accomodate varying types of aggregates having varying precious metal contents, and different rates of water flow.